Slate raised at least $111 million in Series A financing, including an undisclosed amount from Bezos. Slate then raised $600 million in 2024 from Mark Walter, the controlling owner of the Los Angeles Dodgers and CEO of Guggenheim Partners, Jeff Bezos, and General Catalyst, a venture capital firm.[5] In mid-2026, the company said it had completed a $650m series C investment round, which took its total capital raised to $1.4bn.[6]
And if that is still not enough for you, here is an article that explains in details how this is all an Amazon initiative
https://techcrunch.com/2025/04/08/inside-the-ev-startup-secretly-backed-by-jeff-bezos/